As an electric appliance becomes smaller in size, so does a space inside a case of the electric appliance in which air flows. To cool an interior of the small case, a fan with features of a large amount of air and a high static pressure is called for. As a fan with such features, an axial-flow fan with double impellers rotating in mutually opposite directions has come to be used in recent years.
For example, U.S. Pat. No. 6,244,818 and Japanese Patent Laid-Open Publication No. 2000-257597 show a fan which comprises a first axial-flow fan unit having a first impeller with nine front blades, a second axial-flow fan unit having a second impeller with nine rear blades, and a case having 13 stationary blades installed between the two axial-flow fan units. This fan can be transformed into an axial-flow fan with double impellers rotating in mutually opposite directions by rotating the first impeller of the first axial-flow fan unit and the second impeller of the second axial-flow fan unit in mutually opposite directions so as to discharge air drawn in by the first axial-flow fan unit from the second axial-flow fan unit.
In recent years some applications call for higher performance than that of the existing axial-flow fan with double impellers rotating in mutually opposite directions.
In the above-described fan, a first case of the first axial-flow fan unit is combined with a second case of the second axial-flow fan unit through a simple coupling structure. For example, a hook attached to one case is fitted in a fitting groove in the other case, and the two cases are rotated relative to each other to engage the hook of one case with the fitting groove of the other case. With this engaging structure, however, an application of a force acting in a direction reverse to the direction in which the two cases were rotated for coupling can easily disengage the two cases.
An object of the present invention is to provide an axial-flow fan with double impellers rotating in mutually opposite directions which is capable of producing a larger amount of air and a higher static pressure than conventional fans do.
Another object of the present invention is to provide an axial-flow fan with double impellers rotating in mutually opposite directions which has a smaller number of parts than that of conventional fans.
Still another object of the present invention is to provide an axial-flow fan with double impellers rotating in mutually opposite directions which produces smaller noise.
Yet another object of the present invention is to provide an axial-flow fan with double impellers rotating in mutually opposite directions in which the first case of the first axial-flow fan unit and the second case of the second axial-flow fan unit are not easily disconnected if they are subjected to a force acting in a direction reverse to the direction in which the two cases were rotated for coupling.